Field of the Invention
The present invention relates to a method, system, and program for managing resources for competing tasks including operations, operation requests, or processes.
Description of the Related Art
Computing systems often include one or more host computers (“hosts”) for processing data and running application programs, direct access storage devices (DASDs) for storing data, and a storage controller for controlling the transfer of data between the hosts and the DASD. Storage controllers, also referred to as control units or storage directors, manage access to a storage space often comprised of numerous hard disk drives connected in a loop architecture, otherwise referred to as a Direct Access Storage Device (DASD). Hosts may communicate Input/Output (I/O) requests to the storage space through the storage controller.
To maintain availability in the event of a failure, many storage controllers known in the prior art provide redundant hardware clusters. Each hardware cluster comprises a processor complex, cache, non-volatile storage (NVS), such as a battery backed-up Random Access Memory (RAM), and separate power supply to provide connection paths to the attached storage. The NVS in one cluster backs up write data from the cache in the other cluster so that if one cluster fails, the write data in the cache of the failed cluster is stored in the NVS of the surviving cluster. After one cluster fails, all Input/Output (I/O) requests would be directed toward the surviving cluster. When both clusters are available, each cluster may be assigned to handle I/O requests for specific logical storage devices configured within the physical storage devices.
In performing these and other tasks, a cluster can not only execute operations locally using the capabilities of the local cluster itself, but can also make a request to have an operation executed on a remote cluster in the storage controller system. Moreover, each storage controller may have an adapter to communicate over a network with a host computer or another storage controller. For example, the write instructions from the primary storage controller to a secondary storage controller may be generated by a processor of the adapter of the primary storage controller and issued over the network to the secondary storage controller.
Each operation may consume a significant portion of the resources of the cluster or adapter which is performing the requested operation. These resources may include the bandwidth of a bus or the bandwidth of a network connection, as well as the computational capabilities of the processors of the cluster or adapter.
Various techniques have been used to manage the allocation of resources so that operations proceed in an appropriate fashion. For example, operations may be assigned a priority such as low, medium or high. A high priority operation tends to receive a resource more quickly than a medium priority operation which tends to receive a resource more quickly than a low priority operation. However, in order to prevent higher priority operations from blocking the execution of all lower priority operations, various schemes have been used to ensure that a certain minimum number or proportion of lower priority operations are permitted to proceed. For example, the number of operations of each priority type may be counted and higher priority operations may be deferred on occasion to permit a minimum number or proportion of lower priority operations to proceed. Another scheme keeps track of how long a lower priority operation is caused to wait and may increase the priority of the operation as time passes until the operation has sufficient priority to proceed.
Further improvements in allocating resources amongst competing operations may be useful in a variety of applications.